diff --git a/api/src/controllers/UserController.kt b/api/src/controllers/UserController.kt
index df03540..f8800f8 100644
--- a/api/src/controllers/UserController.kt
+++ b/api/src/controllers/UserController.kt
@@ -13,10 +13,7 @@ import io.ktor.request.receive
 import io.ktor.response.respond
 import io.ktor.routing.Routing
 import me.liuwj.ktorm.database.Database
-import me.liuwj.ktorm.dsl.eq
-import me.liuwj.ktorm.dsl.from
-import me.liuwj.ktorm.dsl.select
-import me.liuwj.ktorm.dsl.where
+import me.liuwj.ktorm.dsl.*
 import me.liuwj.ktorm.entity.add
 import me.liuwj.ktorm.entity.sequenceOf
 import org.kodein.di.Kodein
@@ -39,11 +36,11 @@ class UserController(kodein: Kodein) : KodeinController(kodein) {
                 .where { Users.username eq credential.username }
                 .map { row -> row[Users.email]!! to row[Users.password]!! }
                 .firstOrNull()
-                ?: return@post call.respond(HttpStatusCode.BadRequest, ApiError.InvalidCredentialError())
+                ?: return@post call.respond(HttpStatusCode.BadRequest, ApiError.InvalidCredentialError)
 
 
             if (!BCrypt.checkpw(credential.password, password)) {
-                return@post call.respond(HttpStatusCode.BadRequest, ApiError.InvalidCredentialError())
+                return@post call.respond(HttpStatusCode.BadRequest, ApiError.InvalidCredentialError)
             }
 
             return@post call.respond(Response(simpleJwt.sign(email)))
@@ -54,8 +51,14 @@ class UserController(kodein: Kodein) : KodeinController(kodein) {
 
             val user = call.receive<SignUpInfo>()
 
-            // TODO check if user does not already exists
-            // db won't let you insert it anyway
+            val exists = db.from(Users)
+                .select()
+                .where { (Users.username eq user.username) or (Users.email eq user.email) }
+                .any()
+
+            if (exists) {
+                return@post call.respond(HttpStatusCode.Conflict, ApiError.ExistingUserError)
+            }
 
             val hashedPassword = BCrypt.hashpw(user.password, BCrypt.gensalt())
 
@@ -68,7 +71,7 @@ class UserController(kodein: Kodein) : KodeinController(kodein) {
 
             db.sequenceOf(Users).add(newUser)
 
-            call.respond(HttpStatusCode.Created, Response("User created successfully"))
+            return@post call.respond(HttpStatusCode.Created, Response("User created successfully"))
         }
     }
 
diff --git a/api/src/errors/Errors.kt b/api/src/errors/Errors.kt
index 8363139..8f6af26 100644
--- a/api/src/errors/Errors.kt
+++ b/api/src/errors/Errors.kt
@@ -1,5 +1,6 @@
 package be.vandewalleh.errors
 
 sealed class ApiError(val message: String){
-    class InvalidCredentialError : ApiError("Invalid credentials")
+    object InvalidCredentialError : ApiError("Invalid credentials")
+    object ExistingUserError : ApiError("User already exists")
 }